1. Field of the Invention
The present invention is directed towards a system for measuring the quantity of liquid fuels contained in a tank, more particularly of the levels of gasoline and water (at the bottom) in fuel tanks, by using sonic pulses in two tubular sensors. Sound pulses travel in air with small amounts of water vapor or gasoline vapor as the case may be and measure the location of the water level or gasoline level to high accuracy by a time-of-flight method. The transducers used do not contact either gasoline or water.
2. Description of the Prior Art
The oldest method of finding a liquid level is by the use of a dipstick graduated with markings. The method is cumbersome and does not provide a continuous readout.
Ultrasonic ranging systems can be used to detect liquid levels. The system `Tank Gauging Systems and Methods` by Haynes, U.S. Pat. No. 4,805,453, is a good example of a device that provides remote readout continuously. In this system several reflectors spaced at suitable intervals are used as markers. By a time-of-flight method, speeds of sound are measured in gasoline and water at various regions and then converted to an average speed of sound in gasoline. The surface level is determined from the measured time-of-flight and the average speed of sound. A thermometer is used for calibration purposes near the ultrasonic transducer immersed in gasoline, near the bottom of the tank. A large number of reflectors are used in this method because at least one reflector must be present between the surface of gasoline and the transducer used for calibration.